This application claims the priority benefit of Taiwan application Ser. No. 92116501, filed on Jun. 18, 2003.
1. Field of Invention
The present invention relates to a polishing pad and a process of chemical mechanical polishing use thereof. More particularly, the present invention relates to a polishing pad and a process of chemical mechanical polishing use thereof to cut down the processing time and cost.
2. Description of Related Art
Due to market demand, the development trend of semiconductors is towards smaller-scale. The exposure resolution must be improved to meet the requirements of fabricating small-scale semiconductors. A light with shortened wavelength serving as the light source is a means of improving the exposure resolution, but this means leads to shallow depth of focus. Accordingly, the level of the topographic surface of the wafer must be further planarized to solve the problem of shallow depth of focus. Chemical mechanical polishing (CMP) is the most important planarization technique, because it provides a global planarization of the wafer surface. Chemical mechanical polishing process can be used, for example, for forming a shallow trench isolation, a dual damascene structure, a micro-electromechanical system or a panel display.
In the process of fabricating a shallow trench isolation, a chemical mechanical polishing process is performed to polish the silicon oxide layer filled into a trench. However, in case the pattern density of the silicon oxide layer is non-uniform, the polishing rate of the regions with a high density pattern is faster than the polishing rate of the regions with a low density pattern. In addition, the polishing selectivity of silicon oxide to silicon nitride mask layer is low when the slurry abrasive is silica, which is generally used in the polishing process. Accordingly, the silicon oxide layer and the silicon nitride mask layer in the regions with a high density pattern are over polished, leading to a dishing effect. Hence, the uniformity of the device is seriously affected. In order to prevent this problem, a photolithographic process using a reverse-tone mask and an etching process are preformed for patterning the silicon oxide layer to uniform pattern density before the silicon oxide layer is polished. However, an additional mask, an additional photographic process and an additional etching process are required, so that the fabricating process become complicated and the cost is increased.
Currently, a new slurry is used for polishing the filled silicon oxide in the shallow trench isolation, wherein the slurry mainly includes abrasives made of CeO2. Using this slurry, the polishing selectivity of silicon oxide to silicon nitride is very high, so that the mask layer made of silicon nitride can avoid the over removing problem even without performing the additional photolithographic process using the reverse-tone mask and the additional etching process.
However, some problems exist in the chemical mechanical polishing process using the slurry including CeO2 abrasive, which are as follows. FIGS. 1A to 1C are schematic, cross-sectional views, illustrating the chemical mechanical polishing process using the CeO2 slurry according to the prior art. Referring to FIG. 1A, a substrate 100 is provided, wherein the substrate 100 has a layer to be polished 102 having an uneven topographic surface formed thereon. A surface of the substrate 100, with the layer to be polished 102 formed thereon, is placed facing the polishing pad 110 on a polishing machine, simultaneously, slurry with the CeO2 abrasives 120 is supplied to the polishing pad 110.
Thereafter, referring to FIG. 1B, a polishing process is performed. First, the CeO2 abrasive 120 is filled in the gap between raised parts of the layer to be polished 102. Thereafter, polishing of the layer 102 begins after the gap is filled with the CeO2 abrasives 102 as shown in FIG. 1C.
In other words, the step of filling the CeO2 abrasive 120 in the gap and the step of polishing the layer 102 are not performed simultaneously. A polishing effect is produced after the gap is filled with the CeO2 abrasives 120, but no effective polishing occurs during the filling of the CeO2 abrasive 102 into the gap.
The step of filling the CeO2 abrasive 102 into the gap consumes a long time before the polishing process is performed; and consequently, time cost and process cost are very high.
The invention provides a chemical mechanical polishing process to decrease the consumption of abrasives of a slurry.
The invention provides a chemical mechanical polishing process to cut down the process cost and decrease the processing time.
The invention provides a chemical mechanical polishing process to prevent dishing effect.
The present invention provides a chemical mechanical polishing to a substrate having a layer thereon. A pre-polishing process is performed to partially remove raised parts of the layer before conducting a polishing process. Physical properties of the first polishing pad used in the pre-polishing process are different from those of the second polishing pad using in the polishing process and the first polishing pad is not a nonwoven fabric layer. Comparing to the second polishing pad, the first polishing pas has a lower hardness, a lower density, a higher porosity and a rougher surface roughness.
According to an embodiment of this invention, the first polishing pad has the following properties: i. a hardness of 30-35 Shore D; ii. a density of 0.30-0.40 g/cm3; iii. a compressibility of 2.0-3.0%; and iv. a rebound of 70-100%.
The second polishing pad has the following properties: i. a hardness of 50-65 Shore D; ii. a density of 0.60-0.80 g/cm3; iii. a compressibility of 2.0-3.0%; and iv. a rebound of 70-100%.
The slurry abrasive material used in the pre-polishing process and the polishing process includes CeO2. In addition, the first polishing pad and the second polishing pad of this invention can be integrated into a polishing pad having two regions. The first region of the two regions, which is formed of a soft material, is used in the first stage chemical mechanical polishing process, and the second region of the two regions, which is formed of hard material, is used in the second stage chemical mechanical polishing process.
The present invention further provides a planarization process of a semiconductor device to polish a substrate having a layer to be polished thereon. First, slurry is applied to a first polishing pad and the substrate is arranged on the first polishing pad, wherein a material of the first polishing pad is flexible. A first stage polishing process is performed to remove raised parts of the layer to be polished. Thereafter, a second slurry is applied to a second polishing pad and the substrate is placed on the second polishing pad, wherein the first polishing pad is softer than the second polishing pad. A second stage polishing process is conducted to further planarize the layer to be polished.
In the present invention, since the first polishing pad is flexible, porous and with low density, the first polishing pad can be deformed to increase contact areas between the first polishing pad and the raised part of the layer to be polished, and the abrasives easily fill into holes of the surface of the first polishing pad. Ultimately, the layer to be polished can be polished directly during the first stage polishing process, and the time spent waiting for abrasives to fill into the gaps between the raised parts can be saved. Moreover, the consumption of the slurry can be decreased. The slurry abrasives are very expensive, therefore, the process cost can be cut down substantially.
In addition, CeO2 slurry abrasives can be used with this invention used for polishing a silicon oxide layer of a shallow trench isolation fabrication. Using the slurry, the polishing selectivity of silicon oxide to silicon nitride is very high, so that the dishing effect still can be avoided without performing the additional photolithographic process using the reverse-tone mask and the additional etching process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.